1. Field of the Invention
The present invention related generally to the control circuits, and its application in display diagnostics and protection, in Cathode Ray Tube (CRT) based display systems, including but not limited to color monitors, monochrome monitors, computer color terminals, computer monochrome terminals, televisions, hi-definition television, and moniputers.
2. Description of the Prior Art
In the present day design, CRT (Cathode Ray Tube) based display systems are controlled primarily by analog circuit. Digital method plays only a minor role in such systems. With current technology, digital controller's assignment ends with the setting of static parameters. Current displays do not employ any intelligent circuit for protection and diagnostic purpose.
When a multisync monitor is switched from high resolution operation to low resolution operation, the sudden drop in frequency will subject the horizontal output transistor to very high voltages for some time until the power supply to the horizontal section reacted to the change. During this time period the horizontal output transistor is operating outside of the Safe Operating Area (SOA) defined by the transistor maker. Repeated excursion out of SOA degrades the reliability of the transistor.
Violation of SOA operation has been identified as the major failure mode for display systems. SOA circuit and other self test capabilities are absent from current display systems due to the high cost of implementation. When a display system fails, there is no diagnostic information available to a user or service personal. Display repair and service is a task that is difficult to learn and difficult to do.